Heat-sensitive recording material

ABSTRACT

A heat-sensitive recording material having a heat-sensitive recording layer on a substrate. An outermost layer from the substrate contains microparticle-aggregation particles. The microparticle-aggregation particles are preferably formed by silica microparticles, and the outermost layer is preferably a protective layer. The microparticle-aggregation particles have hardness such that soiling of a thermographic printing head is low, and softness such that wear of the thermographic printing head is low.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a heat-sensitive recordingmaterial having a heat-sensitive recording layer on a substrate, andmore particularly to a heat-sensitive recording material suitable forrecording using a heating element such as a thermal head or the like.

[0003] 2. Description of Related Art

[0004] In recent years, heat-sensitive recording has rapidly grown inpopularity, because of benefits such as: 1) no need for development; 2)when paper is used as a substrate, the recording material is verysimilar to ordinary paper; 3) easy handling; 4) high color density; 5)simple and inexpensive recording devices; 6) no noise during recording;7) high reliability, meaning low maintenance; and the like.

[0005] Against this background, there has also been rapid progress inthe shift to color imaging, and demand is high for multi-colorheat-sensitive recording materials that can be directly recorded withthermal heads and the like.

[0006] In heat-sensitive recording, a recording surface of aheat-sensitive recording material is directly contacted by a heatingelement such as a thermal head or the like. In this state, heat isgenerated and the heating causes color development. The heating elementis switched between on and off states and an image is thereby recorded.Accordingly, if runnability (transportability) of the recording materialduring recording is to be improved, or if adhesion of dirt to a surfaceof the thermal head must be avoided, microparticles, which are inorganicparticles or the like, are generally provided at an outermost layer ofthe recording material, which contacts the thermal head.

[0007] However, in order to avoid a reduction in not only heattransmission to the recording material during recording but also imagequality, which depends on heat transmitted, a certain amount of contactpressure is applied and the head is pressed against the recordingmaterial. As a result, wearing tends to occur. In particular, if thereare many high-hardness inorganic particles at the surface of theoutermost layer, wearing of the thermal head (head-wearing) is rapid,and durability thereof is greatly reduced. Wearing of the thermal headis particularly noticeable in cases where application of heat isperformed at a high temperature to obtain high color density and whereheat is applied continuously for multi-color recording.

[0008] Wear can be moderated and the durability of the head improved bytechniques that reduce the above-described head-wearing. Thesetechniques include reducing contact pressure, and making the surfacewith which the head contacts softer by using microparticles with acomparatively low hardness or the like. However, these techniques tendto increase amounts of dirt at the thermal head (head-soiling).Head-soiling inhibits the transfer of heat to the recording material,and interferes with homogeneous color formation. Therefore, in order toobtain sharp images with homogeneous density, it is desirable thathead-soiling tends not to occur.

[0009] Accordingly, head-wearing and head-soiling have a reciprocalrelationship, such that when one is improved, the other tends todeteriorate. Until now it has proved difficult to improve both at thesame time.

[0010] In accordance with the foregoing, a heat-sensitive recordingmaterial that can record, stably over long periods, sharp images withexcellently homogeneous density, that alleviates head-wearing and doesnot reduce durability, and that does not lead to a loss of image qualitydue to head-soiling has been desired.

SUMMARY OF THE INVENTION

[0011] The present invention is provided to solve the above-describedvarious problems of the conventional art, and the goal of the presentinvention is to achieve the following object.

[0012] An object of the present invention is to provide a heat-sensitiverecording material that is capable of stably recording sharp images withexcellently homogeneous density and suppressing head-wearing withoutcausing loss of image quality due to head-soiling.

[0013] The inventor of the present invention has performed assiduousinvestigations into effects of recording surfaces on thermal heads. Theinventor has combined results thereof and has discovered that, while thepresence of microparticles at the surface contacting the head isessential for runnability, it is necessary that the microparticles havehardness such that head-soiling does not occur and softness (pressureabsorbence) such that the head is not scratched.

[0014] The present invention is a heat-sensitive recording materialhaving a heat-sensitive recording layer on a substrate, wherein anoutermost layer from the substrate contains microparticle-aggregationparticles.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] A heat-sensitive recording material of the present inventionincludes microparticle-aggregation particles in an outermost layer,which contacts with a heating element such as a thermal head or the likeduring recording.

[0016] The heat-sensitive recording material of the present invention isdescribed in detail below.

[0017] The heat-sensitive recording material of the present inventionhas, on a substrate, at least a heat-sensitive recording layer. Theheat-sensitive recording material preferably also has a protectivelayer. The heat-sensitive recording material has other layers, such asan intermediate layer and the like, as necessary.

[0018] The present invention includes microparticle-aggregationparticles in the outermost layer provided on the substrate, that is, thelayer disposed furthest from the substrate (which may be aheat-sensitive recording layer or a protective layer). Further, theheat-sensitive recording layer may be a single-color heat-sensitiverecording layer formed by a single layer, or may be a multi-colorheat-sensitive recording layer in which a plurality of single-colorheat-sensitive recording layers that develop mutually different hues arestacked.

[0019] Microparticle-Aggregation Particles

[0020] The microparticle-aggregation particles are regular or irregularparticle aggregations formed by aggregating pluralities ofmicroparticles. More fundamentally, a microparticle-aggregation particlemay be a particle in which some microparticles have been mutuallychemically bonded (e.g., by siloxane bonds or the like). Alternatively,the microparticle-aggregation particle may be a particle in which somemicroparticles have been attracted together by interaction forcesbetween individual microparticles or the like, cohered and aggregated,and held together to form a single particle.

[0021] The microparticle-aggregation particles also include particles inwhich pluralities of microparticles have been made into microparticleaggregations by a binder having elasticity and softness, to therebyprovide aggregation particles provided with sufficient softness to bepressure-deformable, as described below.

[0022] Because the present invention contains themicroparticle-aggregation particles (occasionally hereafter referred toas “aggregation particles”) in the outermost layer, which contacts withthe thermal head, it is possible for a surface of the outermost layer tohave particles that are provided with a certain degree of hardness andwith a softness sufficient to allow pressure-deformation when pressureis applied. That is, the particles have sufficient hardness to preventhead-soiling during recording, but do not have sufficient hardness toscratch and wear the head when a pressing force at or exceeding acertain level is applied at the head. Therefore, head-soiling can beavoided, while at the same time wear of the thermal head can be reduced,even in cases of continuous high-density recording, multi-colorrecording and the like, and thus durability of the head can be greatlyimproved.

[0023] As described earlier, in order to obtain the effects ofpreventing both head-soiling and head-wearing, it is essential that themicroparticle-aggregation particles are present across the whole of thesurface of the outermost layer. Specifically, a total surface coverageof the microparticle-aggregation particles is preferably 20 to 90%, andmore preferably 30 to 70%.

[0024] Consequently, microparticle-aggregation particles relating to thepresent invention do not include aggregates that are effectively onlypartially or locally present in a layer, such as in cases where a layeris formed to include aggregations caused by, for example, a coatingliquid lacking dispersion stability or particles cohering to each otherduring coating or the like, and the like. That is, even if suchaggregations were present in the head-contacting outermost layer,because the aggregations would only be partially or locally present inthe layer, effects of long-term protection of the thermal head fromsoiling and of suppression of wear could not be sufficiently provided.

[0025] In the above, a hardness sufficient for suppressing head-soilingis dependent on the hardness of the microparticles structuring theaggregation particles, and a hardness so as to scratch and wear the headis dependent on the hardness of the aggregation particles themselves.Consequently, simply providing particles in the outermost layer, whichthe head contacts, could not achieve the effects of the presentinvention. However, it is effective to have in the outermost layer anaggregate in which pluralities of particles having sufficient hardnessto prevent soiling are cohered and aggregated by interactionstherebetween, such that the individual particles do not solidify witheach other but deform when pressure is applied, so that frictionalpressure at the head is alleviated.

[0026] In view of the above, provided the microparticle-aggregationparticles are included in the outermost layer on the substrate, themicroparticle-aggregation particles may be provided in any of aheat-sensitive recording layer, a protective layer and the like. Ofthese, if the substrate has both a heat-sensitive recording layer and aprotective layer thereon, the microparticle-aggregation particles arepreferably included in the protective layer.

[0027] The hardness (Mohs' hardness) of the microparticle-aggregationparticles is preferably from 2 to 8, and more preferably from 3 to 7. Ifthe hardness is less than 2, it may not be possible to preventhead-soiling. If the hardness is more than 8, it will be possible toprevent head-soiling but it may not be possible to prevent head-wearing.

[0028] The shapes of the microparticle-aggregation particles may be anyshape, regular or irregular, selected as appropriate. With regard toeffectiveness, aggregation particles formed in a substantially sphericalshape are preferable. Further, the microparticle-aggregation particlesinclude aggregations composed of at least 10 microparticles, andpreferably 100 to 1,000,000 microparticles.

[0029] Moreover, the microparticle-aggregation particles are preferablycomposed of microparticles with a particle size of 0.5 μm or less, morepreferably composed of microparticles with a particle size of 0.2 μm orless, and most preferably composed of microparticles with a particlesize of 0.1 μm or less. If the particle size is more than 0.5 μm,smoothness of the surface will be reduced, and it may be easy for theparticles to detach from the layer surface.

[0030] The microparticle-aggregation particles may be either aggregationparticles composed of inorganic microparticles or aggregation particlescomposed of organic microparticles. With regard to the individualmicroparticles being hard enough to effectively avoid head-soiling,aggregation particles composed of inorganic microparticles arepreferable.

[0031] Examples of the aggregation particles composed of inorganicmicroparticles include aggregation particles composed of microparticlessuch as ultra-fine grain silica, barium sulfate, alumina and the like.Examples of marketed products include SILICA MICROBEAD P500(manufactured by Catalyst & Chemicals Ind. Co. Ltd.); MIZUKASIL P705,P707, P527, P801, etc. (manufactured by Mizusawa Chemical Co., Ltd.);AEROSIL TT600, OX50, etc. (manufactured by Nippon Aerosil Co., Ltd.);and the like.

[0032] Examples of the aggregation particles composed of organicmicroparticles include aggregation particles composed of microparticlessuch as urea resin microparticles, benzoguanamine resin particles andthe like. Examples of marketed products include ORGANIC FILLER(manufactured by Nippon Kasei Chemical Co., Ltd.) and the like.

[0033] Of these, aggregation particles composed of ultra-fine grainsilica, particularly ultra-fine grain silica with a mean particle sizeof 10 to 100 nm (more preferably 10 to 50 nm), are preferable.Furthermore, the particles are preferably substantially spherical. Theaforementioned SILICA MICROBEAD P500 (manufactured by Catalyst &Chemicals Ind. Co. Ltd.) is particularly preferable.

[0034] The microparticle-aggregation particles may contain a single typeof microparticle or a combination of two or more types.

[0035] The mean particle size of the microparticle-aggregationparticles, that is, the mean largest dimension thereof, is preferably0.5 to 10 μm, more preferably 1 to 7 μm, further preferably 1.5 to 5 μm,and most preferably 2 to 3 μm.

[0036] If the mean particle size is less than 0.5 μm, head-soiling mayoccur. If the mean particle size is more than 10 μm, it will be easy forthe microparticle-aggregation particles to detach from the layersurface, and detached microparticle-aggregation particles may adhere toor accumulate on the head, and cause damage to a print surface.

[0037] In cases where glossiness is required, it is preferable to useaggregation particles having a mean particle size toward the large endof the full range (a mean particle size of 1 to 3 μ).

[0038] The mean particle size of the microparticles that structure themicroparticle-aggregation particles and aggregation particles can bemeasured accurately using electron microscopy, but can be measured moreeasily using laser scattering.

[0039] In order to avoid both head-soiling and head-wearing as describedabove, the microparticle-aggregation particles should be contained in arange as follows.

[0040] An amount of the microparticle-aggregation particles present inthe outermost layer of the heat-sensitive recording material ispreferably 0.01 to 1.0 g/m², and more preferably 0.05 to 0.5 g/m². Ifthe amount present is less than 0.01 g/m², it may not be possible toavoid both head-soiling and head-wearing. If the amount present is morethan 1.0 g/m², sensitivity may be reduced and head-wearing may beunexpectedly worsened rather than improved.

[0041] By including the microparticle-aggregation particles in theoutermost layer as described above, head-soiling can be avoided, at thesame time wear of the thermal head can be reduced, and durability of thethermal head can be greatly improved.

[0042] Next, details are given of each of the layers that structure theheat-sensitive recording material of the present invention.

[0043] Heat-Sensitive Recording Layer

[0044] The heat-sensitive recording layer has at least a color-formingcomponent. The heat-sensitive recording layer may be a single-layersingle-color heat-sensitive recording layer, or may be a multi-colorheat-sensitive recording layer in which a plurality of single-colorheat-sensitive recording layers that form mutually different hues arestacked. If a heat-sensitive recording layer forms the outermost layerand is composed of a plurality of layers, the microparticle-aggregationparticles are contained only in the outermost layer thereof.

[0045] Further, the heat-sensitive recording layer includes othercomponents as necessary, such as a basic material, a sensitizer and thelike.

[0046] Color-Forming Component and the Like

[0047] The color-forming component may be a two-component color source(a color-forming component and a compound that causes color formation),such as in combination examples (a) to (r) following. (In each of theseexamples, the first component given is the color-forming component andthe second is the compound that causes color formation.)

[0048] (a) A combination of a photodecomposable diazonium salt compoundand a coupling component (below referred to as a “coupler” whereappropriate).

[0049] (b) A combination of an electron-donating dye precursor and anelectron-accepting compound.

[0050] (c) A combination of a metal salt of an organic acid, such assilver behenate, silver stearate or the like, and a reducing agent, suchas protocatechuic acid, spiroindane, hydroquinone or the like.

[0051] (d) A combination of an iron salt of a long-chain fatty acid,such as ferric stearate, ferric myristate or the like, and a phenol,such as tannic acid, gallic acid, ammonium salicylate or the like.

[0052] (e) A combination of a heavy metal salt of an organic acid, suchas a nickel, cobalt, lead, copper, iron, mercury or silver salt ofacetic acid, stearic acid, palmitic acid or the like, and a sulfide ofan alkali metal or alkaline earth metal, such as calcium sulfide,strontium sulfide, potassium sulfide or the like; or a combination of aheavy metal salt of an organic acid as described above and an organicchelating agent, such as s-diphenyl carbazide, diphenyl carbazone or thelike.

[0053] (f) A combination of a heavy metal sulfate, such as a sulfate ofsilver, lead, mercury, sodium or the like, and a sulfur compound, suchas sodium tetrathionate, sodium thiosulfate, thiourea or the like.

[0054] (g) A combination of an aliphatic ferric salt, such as ferricstearate or the like, and an aromatic polyhydroxy compound, such astetrakis (3,4-dihydroxyphenyl) methane or the like.

[0055] (h) A combination of a metal salt of an organic acid, such assilver oxalate, mercury oxalate or the like, and an organic polyhydroxycompound, such as polyhydroxy alcohol, glycerin, glycol or the like.

[0056] (i) A combination of a ferric salt of a fatty acid, such asferric pelargonate, ferric laurate or the like, and a thiocetylcarbamide or isothiocetyl carbamide derivative.

[0057] (j) A combination of a lead salt of an organic acid, such as leadcaproate, lead pelargonate, lead behenate or the like, and a thioureaderivative, such as ethylene thiourea, N-dodecyl thiourea or the like.

[0058] (k) A combination of a heavy metal salt of a higher fatty acid,such as ferric stearate, copper stearate or the like, and zincdialkyldithiocarbamate.

[0059] (l) A combination that forms an oxazine dye, such as acombination of resorcin and a nitroso compound.

[0060] (m) A combination of a formazan compound and a reducing agentand/or metal salt.

[0061] (n) A combination of a protected dyestuff (or leuco dyestuff)precursor and a protection-removing agent.

[0062] (o) A combination of an oxidation-type color-forming agent and anoxidizer.

[0063] (p) A combination of a phthalonitrile and a diiminoisoindoline (acombination that generates phthalocyanine).

[0064] (q) A combination of an isocyanate and a diiminoisoindoline (acombination that generates a color pigment).

[0065] (r) A combination of a pigment precursor and an acid or a base (acombination that forms a pigment).

[0066] Of these, (a) the combination of a photodecomposable diazoniumsalt compound and a coupler, (b) the combination of an electron-donatingdye precursor and an electron-accepting compound, and (c) thecombination of an organometallic salt and a reducing agent arepreferable in the present invention. Of these, the combinations of (a)and (b) are more preferable, and the combination of (a) is mostpreferable.

[0067] The same applies when the present invention is applied to afull-color heat-sensitive recording material.

[0068] The heat-sensitive recording layer of the heat-sensitiverecording material of the present invention can have various structuralforms. However, it is preferable that on the substrate there is at leastone layer that is a light-fixing-type heat-sensitive recording layer,which includes as main components a diazonium salt compound and acoupler that performs a coupling reaction with the diazonium saltcompound. In the case of a multi-color recording material, it isdesirable to have heat-sensitive recording layers formed with diazo-typecolor-forming components for each of cyan, yellow and magenta. Moreover,a protective layer may, as necessary, be provided on the heat-sensitiverecording layers at an irradiated light-incidence side, so as to be theoutermost layer. Further, as described earlier, intermediate layers may,as appropriate, be provided between respective recording layers in aheat-sensitive recording layer with a multi-layer configuration.Specific structural forms are described below.

[0069] Examples of other compounds that may be used in a heat-sensitiverecording layer that contains a diazonium salt compound and a couplerinclude a basic material, which accelerates the reaction between thediazonium salt compound and the coupler, a sensitizer, and the like.

[0070] The diazonium salt compound is a compound represented by formula(I) below. The wavelength of maximum absorption of the compound can becontrolled on the basis of position and type of a substituent at the Arsection.

Ar—N₂ ⁺·X⁻  (I)

[0071] (In the formula, Ar represents an aryl group and X⁻represents anacid anion.)

[0072] Examples of the diazonium salt compound include acid anion saltssuch as

[0073] 4-(N-(2-(2,4-di-tert-amylphenoxy)butyryl)piperazino)benzenediazonium,

[0074] 4-dioctylaminobenzene diazonium,

[0075] 4-(N-(2-ethyl hexanoyl)piperazino)benzene diazonium,

[0076] 4-dihexylamino-2-hexyloxybenzene diazonium,

[0077] 4-N-ethyl-N-hexadecylamino-2-ethoxybenzo diazonium,

[0078] 3-chloro-4-dioctylamino-2-octyloxybenzene diazonium,

[0079] 2,5-dibutoxy-4-morpholinobenzene diazonium,

[0080] 2,5-dioctoxy-4-morpholinobenzene diazonium,

[0081] 2,5-dibutoxy-4-(N-(2-ethylhexanoyl)piperazino)benzene diazonium,

[0082]2-5-diethoxy-4-(N-(2-(2,4-di-tert-amylphenoxy)butyryl)piperazino)benzenediazonium,

[0083] 2-5-dibutoxy-4-tolylthiobenzene diazonium,

[0084] 3-(2-octyloxyethoxy)-4-morpholinobenzene diazonium and the like,and the diazonium salt compounds shown below (illustrative compounds D-1to D-5).

[0085] Further, hexafluorophosphate salts, tetrafluoroborate salts, and1,5-naphthalene sulfonate salts may be suitably used.

[0086] Of these, preferable compounds, which are photodecomposable bylight at wavelengths of 300 to 400 nm, are

[0087] 4-(N-(2-(2,4-di-tert-amylphenoxy)butyryl)piperazino)benzenediazonium,

[0088] 4-dioctylaminobenzene diazonium,

[0089] 4-(N-(2-ethylhexanoyl)piperazino)benzene diazonium,

[0090] 4-dihexylamino-2-hexyloxybenzene diazonium,

[0091] 4-N-ethyl-N-hexadecylamino-2-ethoxybenzo diazonium,

[0092] 2,5-dibutoxy-4-(N-(2-ethylhexanoyl)piperazino)benzene diazonium,

[0093] 2,5-diethoxy-4-(N-(2-(2,4-di-tert-amylphenoxy)butyryl)piperazino)benzene diazonium

[0094] and the compounds shown as illustrative compounds D-3 to D-5.

[0095] The wavelengths of maximum absorption of the diazonium saltcompounds mentioned here were measured for each compound with aspectrophotometer (Shimazu MPS-2000) for a film of 0.1 to 1.0 g/m².

[0096] Examples of the coupler for colorizing that reacts with thediazonium salt compound when heated include

[0097] resorcin, phloroglucin,

[0098] sodium 2,3-dihydroxynaphthalene-6 sulfonate,

[0099] 1-hydroxy-2-naphthoic acid morpholinopropyl amide,

[0100] 1,5-dihydroxynaphthalene,

[0101] 2,3-dihydroxynaphthalene,

[0102] 2,3-dihydroxy-6-sulfanylnaphthalene,

[0103] 2-hydroxy-3-naphthoic acid anilide,

[0104] 2-hydroxy-3-naphthoic acid ethanol amide,

[0105] 2-hydroxy-3-naphthoic acid octyl amide,

[0106] 2-hydroxy-3-naphthoic acid-N-dodecyloxy propyl amide,

[0107] 2-hydroxy-3-naphthoic acid tetradecyl amide, acetanilide,acetoacetanilide, benzoylacetanilide,

[0108] 2-chloro-5-octylacetoacetanilide,

[0109] 1-phenyl-3-methyl-5-pyrazolone,

[0110] 1-(2′-octylphenyl)-3-methyl-5-pyrazolone,

[0111] 1-(2′,4′,6′-trichlorophenyl)-3-benzamide-5-pyrazolone,

[0112] 1-(2′,4′,6′-trichlorophenyl)-3-anilino-5-pyrazolone,

[0113] 1-phenyl-3-phenylacetamide-5-pyrazolone,

[0114] the couplers shown below (illustrative compounds C-1 to C-6) andthe like. These couplers may be used in combination to obtain a desiredhue.

[0115] The basic material may be an inorganic or organic basic compoundor, alternatively, a compound that decomposes or the like when heatedand thereby releases alkaline material. Representative examples thereofinclude nitrogen-containing compounds such as: organic ammonium salts,organic amines, amides, urea and thiourea, and respective derivativesthereof; thiazoles; pyrroles; pyrimidines; piperazines; guanidines;indoles; imidazoles; imidazolines; triazoles; morpholines; piperidines;amidines; formazines; pyridines; and the like. Specific examples ofthese include tricyclohexylamine, tribenzylamine, octadecylbenzylamine,stearylamine, allylurea, thiourea, methylthiourea, allylthiourea,ethylenethiourea, 2-benzylimid azole, 4-phenylimid azole,2-phenyl-4-methylimi dazole, 2-undecylimidazoline,2,4,5-trifuryl-2-imidazoline, 1,2-diphenyl-4,4-dimethyl-2-imidazoline,2-phenyl-2-imidazoline, 1,2,3-triphenylguanidine,1,2-dicyclohexylguanidine, 1,2,3-tricyclohexylguanidine, guanidinetrichloroacetate, N,N′-dibenzylpiperazine, 4,4′-dithiomorpholine,morpholinium trichloroacetate, 2-aminobenzothiazole,2-benzoylhydrazinobenzothiazole and the like. Two or more of these maybe used in combination.

[0116] Examples of the electron-donating dye precursor includetriarylmethane-type compounds, diphenylmethane-type compounds,thiazine-type compounds, xanthene-type compounds, spiropyran-typecompounds and the like. Of these, triarylmethane-type compounds andxanthene-type compounds are particularly effective with regard to highcolor density.

[0117] Examples include

[0118] 3,3-bis(p-dimethylaminophenyl)-6-dimethylaminophthalide (i.e.,crystal violet lactone),

[0119] 3,3-bis(p-dimethylamino)phthalide,

[0120] 3-(p-dimethylaminophenyl)-3-(1,3-dimethylindole-3-yl)phthalide,

[0121] 3-(p-dimethylaminophenyl)-3-(2-methylindole-3-yl)phthalide,

[0122]3-(o-methyl-p-diethylaminophenyl)-3-(2-methylindole-3-yl)phthalide,

[0123] 4,4′-bis(dimethylamino)benzhydryl benzyl ether, N-halophenylleucoauramine, N-2,4,5-trichlorophenyl leucoauramine,rhodamine-B-anilinolactam, rhodamine (p-nitroanilino) lactam,

[0124] rhodamine-B-(p-chloroanilino)lactam,

[0125] 2-benzylamino-6-diethylaminofluoran,

[0126] 2-anilino-6-diethylaminofluoran,

[0127] 2-anilino-3-methyl-6-diethylaminofluoran,

[0128] 2-anilino-3-methyl-6-cyclohexylmethylaminofluoran,

[0129] 2-anilino-3-methyl-6-isoamylethylaminofluoran,

[0130] 2-(o-chloroanilino)-6-diethylaminofluoran,

[0131] 2-octylamino-6-diethylaminofluoran,

[0132] 2-ethoxyethylamino-3-chloro-2-diethylaminofluoran,

[0133] 2-anilino-3-chloro-6-diethylaminofluoran,

[0134] benzoyl leucomethylene blue, p-nitrobenzyl leucomethylene blue,

[0135] 3-methyl-spiro-dinaphthopyran, 3-ethyl-spiro-dinaphthopyran,

[0136] 3,3′-dichloro-spiro-dinaphthopyran, 3-benzylspirodinaphthopyran,

[0137] 3-propyl-spiro-dibenzopyran and the like.

[0138] Examples of the electron-accepting compound include phenolderivatives, salicylic acid derivatives, hydroxybenzoic esters and thelike. Bisphenols and hydroxybenzoic esters are particularly preferable.

[0139] Examples include

[0140] 2,2-bis(p-hydroxyphenyl)propane (i.e., bisphenol A),

[0141] 4,4′-(p-phenylene diisopropylidene)diphenol (i.e., bisphenol P),

[0142] 2,2-bis(p-hydroxyphenyl)pentane, 2,2-bis(p-hydroxyphenyl)ethane,

[0143] 2,2-bis(p-hydroxyphenyl)butane,

[0144] 2,2-bis(4′-hydroxy-3′,5′-dichlorophenyl)propane,

[0145] 1,1-(p-hydroxyphenyl)cyclohexane, 1,1-(p-hydroxyphenyl)propane,

[0146] 1,1-(p-hydroxyphenyl)pentane,

[0147] 1,1-(p-hydroxyphenyl)-2-ethylhexane,

[0148] 3,5-di(α-methylbenzyl) salicylic acid and polyvalent metal saltsthereof,

[0149] 3,5-di(tert-butyl)salicylic acid and polyvalent metal saltsthereof,

[0150] 3-α,α-dimethylbenzyl salicylic acid and polyvalent metal saltsthereof,

[0151] butyl p-hydroxybenzoate, benzyl p-hydroxybenzoate,

[0152] 2-ethylhexyl p-hydroxybenzoate, p-phenylphenol, p-cumylphenol andthe like.

[0153] A low-melting-point organic compound appropriately containing anaromatic group and a polar group in the molecule thereof can bepreferably used as the sensitizer. Examples include

[0154] benzyl p-benzyloxybenzoate, α-naphthyl benzyl ether,

[0155] β-naphthyl benzyl ether, phenyl β-naphthoate,

[0156] phenyl α-hydroxy- β-naphthoate,

[0157] β-naphthol-(p-chlorobenzyl)ether, 1,4-butanediolphenyl ether,

[0158] 1,4-butanediol-p-methylphenyl ether,

[0159] 1,4-butanediol-p-ethylphenyl ether,

[0160] 1,4-butanediol-m-methylphenylether,

[0161] 1-phenoxy-2-(p-tolyloxy)ethane,

[0162] 1-phenoxy-2-(p-ethylphenoxy)ethane,

[0163] 1-phenoxy-2-(p-chlorophenoxy)ethane, p-benzyl biphenyl and thelike.

[0164] Modes of use of the diazonium salt compound and colorizingcoupler that reacts with the diazonium salt compound when heated, theelectron-donating colorless dye and electron-accepting compound, thebasic material, the sensitizer and the like are not particularlylimited. Examples include (1) a method using a solid dispersion, (2) amethod using an emulsified dispersion, (3) a method using a polymerdispersion, (4) a method using a latex dispersion and (5) a method usingmicrocapsulation. Of these, the method using microcapsulation ispreferable in view of preservability. In particular, if color formationutilizes a reaction between a diazonium salt compound and a coupler, itis preferable that the diazonium salt compound is microcapsulated. Andif color formation utilizes a reaction between an electron-donatingcolorless dye and an electron-accepting compound, it is preferable thatthe electron-donating colorless dye is microcapsulated.

[0165] Microcapsules

[0166] A conventionally known method can be used as a method formicrocapsulating the electron-donating dye precursor or diazonium saltcompound to be used (hereafter sometimes referred to as the“color-forming component”).

[0167] Examples thereof include a method utilizing coacervation of ahydrophyllic wall-forming material, such as disclosed in U.S. Pat. Nos.2,800,457 and 2,800,458; an interfacial polymerization method, such asdisclosed in U.S. Pat. No. 3,287,154, British Patent (GBP) No. 990,443,and Japanese Patent Application Publication (JP-B) Nos. 38-19574, 42-446and 42-771; a polymer precipitation method, such as disclosed in U.S.Pat. Nos. 3,418,250 and 3,660,304; a method using an isocyanate polyolwall material, such as disclosed in U.S. Pat. No. 3,796,669; a methodusing an isocyanate wall material, such as disclosed in U.S. Pat. No.3,914,511; a method using a urea-formaldeyde or urea-formaldehyderesorcinol wall-forming material, such as disclosed in U.S. Pat. Nos.4,001,140, 4,087,376 and 4,089,802; a method using melamine-formaldehyderesin, hydroxy propyl cellulose or the like as a wall-forming material,such as disclosed in U.S. Pat. No. 4,025,455; an in situ method based onmonomer polymerization, such as disclosed in JP-B 36-9168 and JapanesePatent Application Laid-Open (JP-A) No. 51-9079; an electrolyticdispersion cooling method, such as disclosed in GBP 952,807 and GBP965,074; a spray-drying method, such as disclosed in U.S. Pat. No.3,111,407 and GBP 930,422; methods disclosed in JP-B 7-73069, JP-A4-101885 and JP-A 9-263057; and the like.

[0168] The method of microcapsulation is not limited to these methods.However, it is particularly preferable to use an interfacialpolymerization method of dissolving or dispersing the color-formingcomponent in a hydrophobic organic solvent that is to become the core ofthe capsules, to make an oil phase, mixing the oil phase with an aqueousphase in which a water-soluble polymer is dissolved, emulsion-diepersingthe mixture with a homogenizer or the like, and then heating to cause apolymer-forming reaction at oil droplet surfaces and thereby form highpolymer microcapsule walls.

[0169] This interfacial polymerization method can formhomogeneously-sized microcapsules in a short time, and can provide arecording material with excellent raw stock storability.

[0170] In microcapsules that are preferable for the present invention,the microcapsule walls (below referred to simply as “capsule walls”)have a material isolating effect at usual temperatures, so as to preventcontact between materials inside and outside the capsules. It becomespossible for the materials inside and outside to make contact only whena temperature and/or pressure above a certain value is applied. Thischaracteristic can be freely controlled by appropriate selection of acapsule wall material, capsule core material (material held inside thecapsule), additives and the like.

[0171] The capsule wall material for the present invention is addedinside and/or outside the oil droplets.

[0172] Examples of the capsule wall material include polyurethane resin,polyurea resin, polyamide resin, polyester resin, polycarbonate resin,aminoaldehyde resin, melamine resin, polystyrene resin, styreneacrylatecopolymer resin, styrene-methacrylate copolymer resin, gelatin,polyvinyl alcohol and the like. Of these, polyurethane, polyurea,polyamide, polyester and polycarbonate are preferable, and polyurethaneand polyurea are more preferable.

[0173] A combination of two or more of the above may be used for thepolymer material.

[0174] For example, if polyurethane is used as the capsule wallmaterial, a polyvalent isocyanate and a second material that will reacttherewith to form the capsule walls (e.g., a polyol or polyamine) aremixed into the water-soluble polymer solution (the aqueous phase) orinto the oily medium that is to be encapsulated (the oil phase). The oilphase is emulsion-dispersed into the aqueous phase, and thepolymer-forming reaction at the oil droplet surfaces is initiated byheating. Thus, the microcapsule walls are formed.

[0175] Substances disclosed in U.S. Pat. Nos. 3,281,383, 3,773,695,3,793,268, JP-B 48-40347, JP-B 49-24159, JP-A 48-80191 and JP-A 48-84086can be used as the polyvalent isocyanate and the polyol or polyaminethat reacts therewith.

[0176] Some specific examples of the polyvalent isocyanate compound aregiven hereafter. The examples include diisocyanates such as m-phenylenediisocyanate, p-phenylene diisocyanate, 2,6-tolylene diisocyanate,2,4-tolylene diisocyanate, naphthalene-1,4 -diisocyanate,diphenylmethane-4,4′-diisocyanate,3,3′-diphenylmethane-4,4′-diisocyanate, xylene-1,4-diisocyanate,4,4′-diphenylpropane diisocyanate, trimethylene diisocyanate,hexamethylene diisocyanate, propylene-1,2-diisocyanate,butylene-1,2-diisocyanate, cyclohexylene-1,2-diisocyanate,cyclohexylene-1,4-diisocyanate and the like; triisocyanates such as4,4′,4″-triphenylmethane triisocyanate, toluene-2,4,6-triisocyanate andthe like; tetraisocyanates such as4,4′-dimethylphenylmethane-2,2′,5,5′-tetraisocyanate and the like;isocyanate prepolymers such as an adduct of hexamethylene diisocyanateand trimethylol propane, an adduct of 2,4-tolylene diisocyanate andtrimethylol propane, an adduct of xylylene diisocyanate and trimethylolpropane, an adduct of tolylene diisocyanate and hexanetriol, and thelike; and the like. A combination of two or more types thereof may beused as required. Of the above, materials whose molecules contain threeor more isocyanate groups are particularly preferable.

[0177] When the microcapsules are formed, the color-forming componentbeing enclosed may be present inside the capsules in a dissolved stateor in a solid state. If the color-forming component is to be enclosed inthe capsules in a dissolved state, the electron-donating colorless dyeor diazonium salt compound that is the color-forming component should beencapsulated after being dissolved in an organic solvent.

[0178] The organic solvent can generally be appropriately selected fromhigh-boiling-point solvents. Examples thereof include phosphoric esters,phthalic esters, acrylic esters, methacrylic esters, other carboxylicesters, fatty acid amides, alkylated biphenyls, alkylated terphenyls,chlorinated paraffin, alkylated naphthalene, diallylethane, compoundsthat are solid at room temperature, oligomer oils, polymer oils and thelike. Specific examples include organic solvents disclosed in JP-A59-178451 to JP-A 59-178455, JP-A 59-178457, JP-A 60-242094, JP-A63-85633, JP-A 6-194825, JP-A 7-13310, JP-A 7-13311, JP-A 9-106039 andJapanese Patent Application No. 62-75409.

[0179] A usage amount of the organic solvent is preferably from 1 to 500parts by weight for 100 parts by weight of the electron-donatingcolorless dye or diazonium salt compound.

[0180] Further, so-called oilless capsules, in which the above-describedorganic solvent is not used, may be used for encapsulation.

[0181] If solubility in the organic solvent of the electron-donatingcolorless dye or diazonium salt compound to be enclosed is low, theorganic solvent can further be combined with a high-solubilitylow-boiling-point solvent, which serves as an auxiliary solvent.Alternatively, the low-boiling-point solvent can be used and the organicsolvent not used.

[0182] Examples of the low-boiling-point solvent include ethyl acetate,propyl acetate, isopropyl acetate, butyl acetate, methylene chloride andthe like.

[0183] The aqueous solution in which the water-soluble polymer isdissolved is used as the aqueous phase for emulsion-dispersion of theoil phase.

[0184] After the oil phase has been introduced into the aqueous phase,emulsion-dispersion is carried out with a homogenizer or the like. Thewater-soluble polymer is included to serve as a protective colloid forenabling easy, homogeneous dispersion, and also to serve as a dispersantfor stabilizing the emulsion-dispersed aqueous solution. Here, asurfactant can be added to one or both of the oil phase and the aqueousphase in order to further homogenize and stabilize the emulsiondispersion.

[0185] Polyvinyl alcohol or the like can be used as the water-solublepolymer that is included to serve as a protective colloid. The same mayalso be combined with a hydrophobic polymer emulsion, or a latex or thelike.

[0186] Examples of the water-soluble polymer include polyvinyl alcohol,silanol-denatured polyvinyl alcohol, carboxy-denatured polyvinylalcohol, amino-denatured polyvinyl alcohol, itaconic acid-denaturedpolyvinyl alcohol, a styrene-maleic anhydride copolymer, abutadiene-maleic anhydride copolymer, an ethylene-maleic anhydridecopolymer, an isobutylene-maleic anhydride copolymer, polyacrylamide,polystyrene sulfonic acid, polyvinyl pyrrolidone, an ethylene-acrylicacid copolymer, gelatin and the like. Of these, carboxy-denaturedpolyvinyl alcohol is particularly preferable.

[0187] Examples of the hydrophobic polymer emulsion or latex include astyrene-butadiene copolymer, a carboxy-denatured styrene-butadienecopolymer, an acrilonitrile-butadiene copolymer and the like.

[0188] The surfactant can be appropriately selected from among wellknown emulsification surfactants. For example, the surfactant can beappropriately selected from anionic and nonionic surfactants such thatcohesion or precipitation of the above-described protective colloid willnot be caused by an effect of the protective colloid. Specific examplesinclude sodium alkylbenzene sulfonate, sodium alkyl sulfate, sodiumdioctyl sulfosuccinate, polyalkylene glycol (e.g., polyoxyethylene nonylphenyl ether) and the like.

[0189] An addition amount of the surfactant is preferably 0.1 to 5% byweight relative to the weight of the oil phase, and more preferably 0.5to 2% by weight.

[0190] The color-forming component and all other components to beincluded, such as the water-soluble polymer, the sensitizer and othercolor-formation assistants, can be dispersed using solid dispersion bymeans of a sand mill or the like. However, it is preferable to useemulsion-dispersion: first dissolving these components in ahigh-boiling-point organic solvent that is insoluble or hard to dissolvein water, then mixing this solution with a polymer aqueous solution (theaqueous phase) that contains the surfactant and/or the water-solublepolymer that serves as the protective colloid, and emulsifying with ahomogenizer or the like. In this case, a low-boiling-point solvent maybe used as a dissolution assistant.

[0191] Further, the color-forming component and all the other componentsto be included can be respectively separately emulsion-dispersed, or canbe mixed beforehand, dissolved in the high-boiling-point solvent and/orlow-boiling-point solvent, and emulsion-dispersed.

[0192] The size of emulsion dispersion particles formed byemulsion-dispersion is desirably not more than 1 μm.

[0193] Emulsion-dispersion of the oil phase containing the componentsand the aqueous phase containing the surfactant and/or protectivecolloid can be performed easily using a technique of microparticleemulsification such as high-speed stirring, ultrasonic wave dispersionor the like. A known emulsification device can be used; for example, ahomogenizer, a manton gaulin, an ultrasonic disperser, a dissolver, aKADY mill or the like.

[0194] After emulsification, in order to accelerate the capsulewall-forming reaction, the emulsion is heated to between 30 and 70° C.Further, in order to prevent the capsules cohering together during thereaction, addition of water to reduce the number of collisions betweenthe capsules, thorough stirring and the like may be required.

[0195] It is also possible to add a separate, cohesion-preventiondispersion during the reaction.

[0196] Emissions of carbon gas can be observed accompanying progress ofa polymerization reaction. Thus, for the capsule wall-forming reaction,when such emissions finish, it can be seen that the reaction hasfinished.

[0197] Usually, microcapsules enclosing the color-forming component canbe obtained by performing this reaction for a period of several hours.

[0198] For the present invention, the size of the microcapsules ispreferably from 0.1 to 1.0 μm, and more preferably from 0.2 to 0.7 μm.If the size of the formed microcapsules is too small, the surface areafor each unit amount of solid will be large, and a large quantity ofwall material will be required.

[0199] Protective Layer

[0200] The heat-sensitive recording material of the present inventionpreferably further has a protective layer on the heat-sensitiverecording layer, and the protective layer preferably contains themicroparticle-aggregation particles described earlier. That is, if theheat-sensitive recording material has the protective layer, thestructure is such that the protective layer is the outermost layer.

[0201] Details of the amount of the microparticle-aggregation particlesin the protective layer and the like, and of preferable modes and thelike, are as described earlier.

[0202] The protective layer may include microparticles of pigment andthe like. However, because the microparticle-aggregation particles arecontained in the protective layer, both head-soiling and head-wearing ofthe thermal head can be improved together.

[0203] Further, together with the microparticle-aggregation particles,the protective layer has a binder, a pigment, a lubricant, a surfactantand the like. A cross-linking agent, a matting agent, a parting agent, adispersion stabilizer, a water repellent and the like may be included inthe protective layer as necessary. The protective layer may have asingle-layer structure, or may have a laminated structure of two or morelayers. The binder may also be provided with the capability to act as alubricant.

[0204] Binder

[0205] Examples of the binder include polyvinyl alcohol-relatedcompounds such as polyvinyl alcohol, denatured polyvinyl alcohol,alkylether-denatured polyvinyl alcohol and the like; silicone-denaturedpolymers; gelatin; methylcellulose; carboxymethylcellulose;hydroxyethylcellulose; starches; agar; K-carageenan; gum arabic; casein;a hydrolysate of a styrene-maleic anhydride copolymer; a hydrolysate ofan ethylene-maleic anhydride copolymer; a hydrolysate of anisobutylene-maleic anhydride copolymer; polyacrylamide and the like.

[0206] Of these, the polyvinyl alcohol-related compounds and thesilicone-denatured polymers are preferable. Of the polyvinylalcohol-related compounds, the alkylether-denatured polyvinyl alcohol isparticularly preferable. Details thereof can be found in the disclosureof JP-A 2000-118133. Moreover, another of the aforementioned binders maybe combined therewith as necessary.

[0207] If the alkylether-denatured polyvinyl alcohol is used, alkylgroups tend to align at the surface of the protective layer. Thus, acoefficient of kinematic friction of the surface against the thermalhead is lowered, and printing faults are reduced. At the same time, itcan be expected that smoothness (glossiness) of the printing surface andcolor density will improve.

[0208] If a coefficient of static friction of the protective layersurface is lowered, runnability of a medium such as the heat-sensitiverecording material or the like when recording at a printer or the likecan be improved. Moreover, the alkylether-denatured polyvinyl alcohol,being a polyvinyl alcohol, exhibits excellent light resistance and filmstrength. Also, because hydrophobic groups are aligned at the surface,an improvement in water resistance is provided.

[0209] If the alkylether-denatured polyvinyl alcohol is used, the amountthereof included is preferably at least 50% by weight of the totalamount of the binder in the protective layer, and more preferably atleast 80% by weight.

[0210] If the included amount is less than 50% by weight, theabove-described effects of using the alkylether-denatured polyvinylalcohol may not be adequately provided.

[0211] Examples of a silicone-denatured polymer include silicone graftpolymers, silicone block polymers, silicone-denatured acrylic polymers,silicone-denatured polyvinyl alcohol and the like. Of these, thesilicone graft polymers are especially preferable. Suitable examples ofthe silicone graft polymers include silicone graft acrylic polymers andsilicone graft-denatured polyvinyl alcohol.

[0212] That is, a trunk polymer of the silicone-denatured polymer may beany polymer having resin characteristics, that is, having excellentfilm-forming ability, excellent heat resistance, excellent lightresistance, excellent film strength and a high Tg (glass transitiontemperature). Of such polymers, acrylic-type resins and polyvinylalcohol-type resins are preferable.

[0213] Specifically, suitable silicone-denatured polymers are disclosedin JP-A 10-329427.

[0214] The Tg of the silicone-denatured polymer is preferably at least60 ° C., more preferably at least 80 ° C., and most preferably at least100 ° C. If the Tg is less than 60 ° C., lubricity with respect to thehead during printing may be lowered.

[0215] If the silicone-denatured polymer is used, the amount thereofincluded is preferably 5 to 100% by weight of the total amount of thebinder, and more preferably 50 to 90% by weight. If the amount is lessthan 5% by weight of the total amount, adequate heat resistance, lightresistance and film strength may not be obtained.

[0216] Here, in view of obtaining smoothness and glossiness at a textureportion and the printing surface, it is preferable to have a set-dryablewater-soluble polymer in the binder. The set-dryable water-solublepolymer is a water-soluble polymer that causes a coating to exhibit apredetermined viscosity when heated (e.g., to around 40 ° C.) and gels,thereby raising viscosity and terminating a fluid state, duringsubsequent cooling (e.g., to between 5 and 15 ° C.).

[0217] However, it is difficult for a silicone-denatured polymer thatcan provide a preferable binder to exhibit set-dryability if used alone.Consequently, when such polymer is used, it is combined with theset-dryable water-soluble polymer. Thus, the protective layer is formedwith ease.

[0218] If the protective layer is formed by this method, thesilicone-denatured polymer with the relatively high Tg tends to align inthe vicinity of the protective layer surface. Consequently, hardness ishigh at a surface side of the protective layer. Thus, sticking andresidue-adhesion to a heat-sensitive recording head or the like can beprevented, a smoothness-processing effect can be provided to theprotective layer surface by the heat-sensitive recording head or thelike, and a tracking characteristic of the heat-sensitive recording heador the like is improved, such that print failures can be eliminated andcolor density can be raised.

[0219] In view of excellent compatibility, the water-soluble polymercombined with the silicone-denatured polymer is particularly preferablygelatin. A ratio of the silicone-denatured polymer to the gelatin ispreferably a weight ratio from 50/50 to 90/10.

[0220] Further, if a polyvinyl alcohol-type compound is used, ifconsideration is given to compatibility with the silicone-denaturedpolymer, silanol-denatured polyvinyl alcohol is preferable. Moreover,the silanol-denatured polyvinyl alcohol may be used as the set-dryablewater-soluble polymer by combining the silanol-denatured polyvinylalcohol with boric acid or a salt thereof which serves as a gellingagent.

[0221] If the silanol-denatured polyvinyl alcohol and thesilicone-denatured polymer are used, a ratio of the silicone-denaturedpolymer to the silanol-denatured polyvinyl alcohol is preferably aweight ratio from 5/95 to 95/5, and more preferably from 50/50 to 90/10.

[0222] A synthetic rubber latex or a synthetic resin emulsion or thelike can also be used as the binder.

[0223] Examples of monomers structuring the synthetic rubber latex orsynthetic resin emulsion include acrylic ester, methacrylic ester,crotonic ester, vinyl ester, maleic diester, fumaric diester, itaconicdiester, acrylamides, methacrylamides, vinyl ethers, styrenes,acrylonitriles and the like.

[0224] Cross-Linking Agent

[0225] It is also preferable to combine with the binder a cross-linkingagent that causes a cross-linking reaction with the binder.

[0226] Furthermore, it is desirable for the silanol-denatured polyvinylalcohol and/or silicone-denatured polymer to include at least one sortof functional group selected from a carboxy group, an amino group, anammonium salt group, a hydroxy group, a sulfinic acid (or sulfinate)group, a sulfonic acid (or sulfonate) group and a glycidyl group.

[0227] Examples of agents that can be used as the cross-linking agentinclude vinyl sulfone-type compounds, aldehyde-type compounds(formaldehyde, glutaraldehyde, dialdehyde starch and the like),epoxy-type compounds, oxazine-type compounds, triazine-type compounds, apolymer hardening agent disclosed in JP-A 62-234157, methylatedmelamine, blocked isocyanates, methylol compounds, carbodiimide resinsand the like.

[0228] Of these, the vinyl sulfone-type compounds, the aldehyde-typecompounds, the epoxy-type compounds, the oxazine-type compounds, thetriazine-type compounds and the polymer hardening agent disclosed inJP-A 62-234157 are suitable.

[0229] Of the aforementioned denatured polyvinyl alcohols, thesilanol-denatured polyvinyl alcohol, which is capable of improving waterresistance and the like unassisted, is particularly preferable. In orderto further improve water resistance, it is effective to use thecross-linking agent and a catalyst to accelerate the cross-linkingreaction, with the silanol-denatured polyvinyl alcohol.

[0230] Lubricant

[0231] Examples of the lubricant include waxes and silicone oils.

[0232] The wax is a compound that is solid below room temperature andhas a melting point in the range 30 to 200 ° C., and any natural wax orsynthetic wax can be suitably used as the wax. Of these compounds,compounds having a melting point from 50 to 150 ° C. are preferable.

[0233] Examples of natural waxes include vegetable waxes such ascarnauba wax, Japan tallow and the like; animal waxes such as beeswaxand the like; mineral waxes such as montan wax and the like; paraffinwax; oil waxes such as microcrystalline wax and the like; and the like.Examples of synthetic waxes include synthetic hydrocarbon waxes such aspolyethylene wax and the like; denatured waxes such as montan waxderivatives, paraffin wax derivatives and the like; hydrogenated waxessuch as solidified castor oil or the like; montanic ester wax; zincstearate; stearic amide; methylol stearic amide; ethylene bis stearicamide; block polymers of polyethylene and ethoxylated alcohols (e.g.,UNITOX, manufactured by Toyo Petrolite Co., Ltd.); tristearyl phosphate;and the like.

[0234] Of these, zinc stearate is particularly preferable.

[0235] The wax can be used as a solid-dispersed wax. A preferable methodfor regulating the wax dispersion, in view of dispersion stability,light resistance of a coating material (stain resistance) and the like,is a method capable of adsorbing the wax with a low molecular weightdispersant, homogeneously dispersing the wax in a microparticle state,adsorbing and dispersing this dispersion with a high molecular weightdispersant, and removing the low molecular weight dispersant. Examplesof the low molecular weight dispersant include low molecular weightnonionic surfactants, low molecular weight anionic surfactants, lowmolecular weight betaine surfactants and the like. Examples of the highmolecular weight dispersant include high molecular weight surfactants,denatured and undenatured polyvinyl alcohols, water-soluble acrylicresins having acrylic acid or methacrylic acid as a main component,water-soluble cellulose derivatives (e.g., carboxymethylcellulose,etc.), alkyl-terminated polyglycerine and the like.

[0236] An amount of wax included in the wax dispersion is preferably 5to 50% by weight, and more preferably 10 to 35% by weight.

[0237] An amount of wax included in the protective layer is preferably 5to 30% by weight of all solid components in the protective layer, andmore preferably 7 to 20% by weight.

[0238] If an aforementioned silicone oil is to be used and isnon-aqueous, the same can be added as an emulsion. If the silicone oilis aqueous, the same can simply be blended with a coating liquid.

[0239] Pigment

[0240] In order to further improve wear resistance and lubricity, aknown organic or inorganic pigment may be appropriately selected andused.

[0241] Examples of the pigment include calcium carbonate, aluminiumhydroxide, barium sulfate, titanium oxide, talc, agalmatolite, kaolin,calcined kaolin, amorphous silica, urea-formalin resin powder,polyethylene resin powder, benzoguanamine resin powder and the like.These can be used singly, or two or more can be mixed for use.

[0242] With regard to preventing loss of glossiness, it is particularlypreferable if the pigment is inorganic ultra-fine particles. Inorganicultra-fine particles means particles whose mean primary dimension is notmore than 0.1 μm. The particles are not particularly limited providedthe mean size thereof is 0.1 μm or smaller, but a maximum particle sizein a dispersion solution (large-end threshold value of a distribution ofparticle sizes in the dispersion solution) is preferably not more than0.5 μm, more preferably not more than 0.4 μm, and most preferably notmore than 0.35 μm.

[0243] The particle sizes can be measured by a known method, forexample, a COULTER N4 type sub-micron particle analyzer (Nikkaki BiosCo., Ltd.) or the like.

[0244] Examples of the inorganic ultra-fine particles include bariumsulfate, zinc oxide, magnesium oxide, lead oxide, zirconium oxide,colloidal silica, alumina and the like. Of these, barium sulfate,colloidal silica and alumina are preferable. Examples of productsavailable on the market that are inorganic fine particles having a meanprimary particle dimension of not more than 0.1 μm and being suitablefor use in the present invention include: BARIFINE BF-21 (bariumsulfate), BARIFINE BF-20 (barium sulfate) and FINEX-75 (zinc oxide) (allmanufactured by Sakai Chemical Industry Co., Ltd.); NZR-A (zirconiumoxide, manufactured by Nissan Chemical Industries, Ltd.); TTO-55(titanium oxide, manufactured by Ishihara Sangyo Kaisha, Ltd.); silicamanufactured by Nippon Aerosil; and the like

[0245] With regard to production quality and effects of preventingcohering of the microparticles and achieving homogeneous adsorption toresin particle surfaces, preferable methods for blending the inorganicultra-fine particles into a coating liquid for forming the protectivelayer (a protective layer coating liquid) include a method of blendingthe inorganic ultra-fine particles with an aqueous dispersion resin suchas carboxymethylcellulose, gelatin or polyvinyl alcohol to make a resinsolution, a method of blending after the colloid dispersion has beenadjusted in various sorts of mill or the like, and the like.

[0246] A usage amount of the pigment can be suitably selected from arange such that the effects of the present invention are not disrupted.

[0247] Matting Agent

[0248] Examples of the matting agent include microparticles such asstarch particles obtained from barley, wheat, corn, rice, beans and thelike; cellulose fibers; synthetic polymer microparticles such aspolystyrene resins, epoxy resins, polyurethane resins, urea-formalinresins, poly(meth)acrylate resins, polymethyl(meth)acrylate resin,copolymer resins of vinyl chloride, vinyl acetate and the like, andpolyolefin and the like; inorganic microparticles such as calciumcarbonate, titanium oxide, kaolin, aluminium hydroxide, silica, zincoxide and the like; and the like.

[0249] Two or more of these matting agents may be combined.

[0250] The protective layer may be formed by coating the coating liquidfor forming the protective layer onto the heat-sensitive recording layerusing a known device such as a bar coater, an air knife coater, a bladecoater, a curtain coater or the like, and drying the coating. Theprotective layer may be coated at the same time as the heat-sensitiverecording layer, or may be coated onto the heat-sensitive recordinglayer after the heat-sensitive recording layer has been coated and driedfor a period.

[0251] A dry-coat amount of the protective layer is preferably 0.1 to 3g/m², and more preferably 0.3 to 2.0 g/m². If the coating amount is toolarge, heat sensitivity may be significantly reduced. And if the coatingamount is too small, the functions of the protective layer (wearresistance, lubrication, scratch resistance, etc.) will not besufficiently provided. After the protective layer has been coated, acalendering treatment and the like may be applied as necessary.

[0252] Other Layers

[0253] Other layers, such as an intermediate layer, an undercoat and thelike, can be provided in the heat-sensitive recording material of thepresent invention as necessary.

[0254] Intermediate Layer

[0255] If a plurality of heat-sensitive recording layers are to bestacked on the substrate to form a multi-color heat-sensitive recordingmaterial, it is preferable that intermediate layers which arenon-color-forming layers be provided between respective recordinglayers.

[0256] The intermediate layer is mainly formed of a binder. Additivesmay be included as necessary, such as a hardener, a polymer latex, afilter dye, a swellable layer-shaping compound (e.g., swellablesynthetic mica), ultra-fine particles, an ultraviolet absorber and thelike.

[0257] Examples of the binder include, besides the water-soluble polymerused for the encapsulation of the color-forming component, polystyrene;polyvinyl formal; polyvinyl butyral; acrylic resins such as polymethylacrylate, polybutyl acrylate, polymethyl methacrylate and polybutylmethacrylate, and copolymers thereof; solvent-soluble polymers such asphenol resin, styrene-butadiene resin, ethylcellulose, epoxy resin,urethane resin and the like; latexes of the solvent-soluble polymers;and the like.

[0258] Of these, gelatin and polyvinyl alcohol are preferable.

[0259] Undercoat Layer

[0260] In order to prevent the heat-sensitive recording layer peelingoff from the substrate, an undercoat layer can also be provided, betweenthe substrate and the heat-sensitive recording layer.

[0261] Gelatin, polyvinyl alcohol-type compounds, acrylic acid estercopolymers, polyvinylidene chloride, SBR, aqueous polyester and the likecan be used in the undercoat layer. In particular, an undercoat layerdisclosed in JP-A 11-5366, which includes synthetic mica which isswellable by oil, is preferable.

[0262] When the heat-sensitive recording layer is coated and formed onthe undercoat layer, the undercoat layer may be swelled by water contentin the coating liquid, which could cause an image recorded on theheat-sensitive recording layer to deteriorate. Therefore, it ispreferable to harden the undercoat layer using a hardener such as boricacid or the like and a dialdehyde such as glutaraldehyde,2,3-dihydroxy-1,4-dioxane or the like.

[0263] An addition amount of the hardener can be selected, from a rangeof 0.2 to 3.0% by weight of total solids of the undercoat layer, torealize a desired degree of hardness.

[0264] Transmittance-Regulating Layer

[0265] At least one transmittance-regulating layer can be provided inthe heat-sensitive recording material. The transmittance-regulatinglayer is preferably formed between the heat-sensitive recording layerand the outer protective layer. The transmittance-regulating layer maybe integrated with the protective layer to form a dual-purpose layer. Ifthe transmittance-regulating layer is integrated with the protectivelayer, the transmittance-regulating layer, being the outermost layer,contains the microparticle-aggregation particles described earlier.

[0266] Characteristics of the transmittance-regulating layer can befreely selected in accordance with characteristics of alight-fixing-type heat-sensitive recording layer.

[0267] The transmittance-regulating layer contains a component thatfunctions as a precursor of an ultraviolet absorber. This component doesnot function as an ultraviolet absorber until light in a wavelengthrange necessary for fixing has irradiated. Thus, transmittance is highand, when the light-fixing-type heat-sensitive recording layer is to befixed, plenty of light in the necessary wavelength range for fixing istransmitted. Also, visible light transmittance is high, so thetransmittance-regulating layer does not cause failures in fixing of theheat-sensitive recording layer.

[0268] After irradiation onto the light-fixing-type heat-sensitiverecording layer of the light in the necessary wavelength range forlight-irradiation fixing has finished, a reaction of the ultravioletabsorber precursor is caused by heat or light or the like, so that theultraviolet absorber precursor subsequently functions as the ultravioletabsorber. Thus, light in a wavelength range necessary forultraviolet-range fixing is mostly absorbed by the ultraviolet absorber,transmittance is low, and the light resistance of the heat-sensitiverecording layer is improved. However, there is no effect on visiblelight, and visible light transmittance is substantially unchanged. Acompound disclosed in JP-A 9-1928 can be used as the ultravioletabsorber precursor.

[0269] Below, a specific structural mode of a multi-color heat-sensitiverecording material is described.

[0270] The heat-sensitive recording material of the present inventionmay be a multi-color heat-sensitive recording material having aheat-sensitive recording layer with a laminated structure, in whichsingle-color heat-sensitive recording layers are plurally stacked. Forthe multi-color heat-sensitive recording material, a mode is preferablein which at least one of the layers structuring the heat-sensitiverecording layer is a light-fixing-type heat-sensitive recording layerincluding a diazonium salt compound and a colorizing coupler that reactswith the diazonium salt compound. For example, structure may be as inthe modes shown in (a) to (c) following, or the like.

[0271] (a) A heat-sensitive recording material having a heat-sensitiverecording layer in which a first heat-sensitive recording layer (layerA) and a second heat-sensitive recording layer (layer B) are stacked ona substrate. The first heat-sensitive recording layer is alight-fixing-type heat-sensitive recording layer containing a diazoniumsalt compound with a wavelength of maximum absorption of 360±20 nm and acolorizing coupler that reacts with the diazonium salt compound. Thesecond heat-sensitive recording layer is a light-fixing-typeheat-sensitive recording layer containing a diazonium salt compound witha wavelength of maximum absorption of 400±20 nm and a colorizing couplerthat reacts with the diazonium salt compound. A transmittance-regulatinglayer and a protective layer are provided on these layers as necessary.

[0272] (b) A heat-sensitive recording material having a heat-sensitiverecording layer in which a first heat-sensitive recording layer (layerA), a second heat-sensitive recording layer (layer B) and a thirdheat-sensitive recording layer (layer C) are stacked in that order on asubstrate. The first heat-sensitive recording layer is a heat-sensitiverecording layer containing an electron-donating dye and anelectron-accepting compound. The second heat-sensitive recording layeris a light-fixing-type heat-sensitive recording layer containing adiazonium salt compound with a wavelength of maximum absorption of360±20 nm and a colorizing coupler that reacts with the diazonium saltcompound. The third heat-sensitive recording layer is alight-fixing-type heat-sensitive recording layer containing a diazoniumsalt compound with a wavelength of maximum absorption of 400±20 nm and acolorizing coupler that reacts with the diazonium salt compound. Atransmittance-regulating layer and a protective layer are provided onthese layers as necessary.

[0273] (c) A heat-sensitive recording material having a heat-sensitiverecording layer in which a first heat-sensitive recording layer (layerA), a second heat-sensitive recording layer (layer B) and a thirdheat-sensitive recording layer (layer C) are stacked in that order on asubstrate. The first heat-sensitive recording layer is alight-fixing-type heat-sensitive recording layer containing a diazoniumsalt compound with a wavelength of maximum absorption of 340±20 nm and acolorizing coupler that reacts with the diazonium salt compound. Thesecond heat-sensitive recording layer is a light-fixing-typeheat-sensitive recording layer containing a diazonium salt compound witha wavelength of maximum absorption of 360±20 nm and a colorizing couplerthat reacts with the diazonium salt compound. The third heat-sensitiverecording layer is a light-fixing-type heat-sensitive recording layercontaining a diazonium salt compound with a wavelength of maximumabsorption of 400±20 nm and a colorizing coupler that reacts with thediazonium salt compound. A transmittance-regulating layer and aprotective layer are provided on these layers as necessary.

[0274] A method for multi-color recording is explained below withreference to (b) and (c) above.

[0275] Firstly, the third heat-sensitive recording layer (layer C) isheated, and the diazonium salt compound and coupler in layer C formcolor. Then, light with a wavelength of 400±20 nm is irradiated, andunreacted diazonium salt compound contained in layer C is decomposed andlight-fixed. Next, sufficient heat to cause color-forming in the secondheat-sensitive recording layer (layer B) is applied, and the diazoniumsalt compound and coupler in layer B form color. At this time, layer Cis also being heated strongly, but the diazonium salt compound thereinhas already been decomposed (light-fixed). Thus, layer C has lost anycolor-forming ability and does not form color at this time. Then, lightwith a wavelength of 360±20 nm is irradiated, and unreacted diazoniumsalt compound contained in layer B is decomposed and light-fixed.Finally, sufficient heat to cause color-forming in the firstheat-sensitive recording layer (layer A) is applied, and color is formedtherein. At this time, layers B and C are also being heated strongly,but the diazonium salt compounds therein have already been decomposed(light-fixed). Thus, layers B and C have lost any color-forming abilityand do not form color at this time.

[0276] The stacking order of the layers is such that a yellow layer,which has low visibility, is the lowest layer. Consequently, an effectof roughness of the substrate on picture quality can be reduced. This isparticularly worthwhile if an improvement in picture quality is to beachieved.

[0277] Also, if all of the heat-sensitive recording layers (layers A, Band C) are heat-sensitive recording layers containing diazo compounds,although light-fixing must be performed after color formation for layersB and C, light-fixing is not necessarily required for the last layer toundergo image-recording, layer A. However, with regard to improvingpreservation stability of a formed image, it is preferable to performlight-fixing for layer A.

[0278] A fixing light source for light-fixing can be suitably selectedfrom known light sources. Examples thereof include various fluorescentlamps, xenon lamps, mercury lamps and the like. Of these, in view ofhigh efficiency of light-fixing, it is preferable to use a light sourcewhose emission spectrum strongly matches the absorption spectrum of thediazonium salt compound used in the heat-sensitive recording material.

[0279] Moreover, the heat-sensitive recording material of the presentinvention can be used as a heat-development-type photosensitivematerial. First, light-exposure is performed through an originalpositioned over the heat-sensitive recording layer of the heat-sensitiverecording material, to decompose the diazonium salt compound at anon-image portion and form a latent image. Then, the whole of theheat-sensitive recording material is heated and an image is formed.

[0280] The heat-sensitive recording material of the present inventioncan be produced by performing dispersion or dissolution in a solvent foreach component as necessary to thereby make a heat-sensitive recordinglayer coating liquid, a protective layer coating liquid and the like,coating the same onto a desired substrate, and drying.

[0281] The solvent is preferably water. However, an organic solvent thatis capable of mixing with water, such as alcohol, a ketone or the like,can be combined with the water.

[0282] Examples of a coating means for coating the heat-sensitiverecording layer coating liquid include a blade coater, rod coater, knifecoater, roll doctor coater, reverse roll coater, transfer roll coater,gravure coater, kiss roll coater, curtain coater, extrusion coater andthe like. Coating can be performed with reference to a method disclosedin Research Disclosure, Vol. 200 (December 1980, Item 20036, page XV).

[0283] The thickness of the heat-sensitive recording layer is preferably0.1 to 50 μm, and more preferably 5 to 35 μm.

[0284] Examples of the substrate used in the heat-sensitive recordingmaterial include synthetic papers such as neutral paper, acidic paper,coated paper, laminated paper and the like, films such as polyethyleneterephthalate film, cellulose triacetate film, polyethylene film,polystyrene film, polycarbonate film and the like; and metal plates ofaluminum, zinc, copper and the like. These may be subjected to varioustreatments for a substrate surface, such as surface processing,undercoating, metallic vapor processing and the like. A substratedisclosed in Research Disclosure, Vol. 200 (December 1980, Item 20036,page XVII) can also be used.

[0285] Each of these substrates can also have a fluorescent brightener,a blueing dye, a pigment or the like included therein.

EXAMPLES

[0286] The present invention is explained below by Examples. The presentinvention is not limited to these Examples. Hereafter “parts” and “%”signify “parts by weight” and “% by weight”, respectively.

Example 1

[0287]1) Preparation of a Substrate

[0288] Wood pulp composed of 100 parts of LBKP was beaten to a CanadianFreeness of 300 cc by a double disc refiner. To the pulp were added 0.5parts of epoxidized behenic acid amide, 1.0 part of anionicpolyacrylamide, 0.1 parts of polyamidepolyamine-epichlorohydrin and 0.5parts of cationic polyacrylamide, each ratio being absolute dry weightrelative to the weight of the pulp. This pulp was fed to a long-meshpaper machine to produce base paper having a weight of 100 g/m². Thebase paper was sized with 1.0 g/m² absolute dry weight of polyvinylalcohol and was adjusted to a specific gravity of 1.0 by calendering toprovide foundation paper.

[0289] A wire-facing side (back side) of this paper was subjected tocorona discharge treatment, and was then coated by a melt-extruder to athickness of 30 μm with a high-density polyethylene resin. Thus, a resinlayer having a matte surface was formed (this face is hereafter referredto as “back face”). The polyethylene-coated back face side was subjectedto corona discharge treatment, and was then coated with an anti-staticagent, which was an aqueous dispersion of aluminum oxide (ALUMINA SOL100, produced by Nissan Chemical Industries, Ltd.) and silicon dioxide(SNOWTEX O, produced by Nissan Chemical Industries, Ltd.) in a 1:2weight ratio, such that the weight of this coating after drying would be0.2 g/m² (thus providing a PE-backed laminate).

[0290] A felt face side was a side of the base paper (which had beenprovided with the resin layer) at which the resin layer was notprovided. The felt face side was subjected to corona dischargetreatment, and was then coated by a melt-extruder to a thickness of 40μm with a low-density polyethylene resin containing 10% titanium dioxideand a trace amount of ultramarine. Thus, a resin layer having a glossysurface was formed (this face is hereafter referred to as “front face”).The polyethylene-coated front face side was subjected to coronadischarge treatment and was then coated with a gelatin undercoat suchthat the weight of this coating after drying would be 0.1 g/m².

[0291] Accordingly, resin layers were formed at both the front and backof the base paper, and a paper substrate was obtained.

[0292] 2) Preparation of a Coating Liquid for an Undercoat Layer

[0293] 97.5 parts of water and 2.5 parts of a synthetic mica that isswellable by oil (ME 100, produced by Co-op Chemical Co. Ltd.) weredispersed together in a dyno mill. This dispersion was added to 200 g ofa 5% aqueous solution of gelatin at 40 ° C., and stirred for 30 minutes.Then, 20 cc of a 5% aqueous solution of surfactant-1, shown below, wasadded. Thus, the coating liquid for the undercoat layer was provided.

[0294] 3) Preparation of a Coating Liquid for a Cyan Heat-SensitiveRecording Layer

[0295] Preparation of an Electron-Donating Dye Precursor-EncasingMicrocapsule Liquid

[0296] {circle over (1)} Liquid A

[0297] 5 parts of3-(o-methyl-p-dimethylaminophenyl)-3-(1′-ethyl-2′-methylindole-3-yl)phthalide(the electron-donating dye precursor) was dissolved in 20 parts of ethylacetate. To this solution was added 20 parts of alkyl naphthalene (ahigh-boiling-point solvent), and this was heated and homogeneouslymixed.

[0298] To the resulting solution was added 20 parts of a 1:3 weightedadduct of xylylene diisocyanate and trimethylol propane. The solutionwas homogeneously stirred and liquid A was obtained.

[0299] {circle over (2)} Liquid B

[0300] 2 parts of a 2% aqueous solution of sodium dodecylsulfonate wasadded to 54 parts of a 6% aqueous solution of phthalated gelatin. Thus,liquid B was obtained.

[0301] Liquid A was added to liquid B, and emulsion-dispersed using ahomogenizer to obtain an emulsion dispersion. 68 parts of water wasadded to this emulsion dispersion and homogeneously mixed. Then thismixture was heated to 50 ° C. while being stirred. An encapsulationreaction was carried out for 3 hours so as to produce microcapsuleshaving a mean particle size of 1.2 μm. Thus, the electron-donating dyeprecursor-encasing microcapsule solution was obtained.

[0302] Preparation of an Emulsion Dispersion of a Developer

[0303] 2.5 parts of 1,1-(p-hydroxyphenyl)-2-ethylhexane (a developer),0.3 parts of tricresyl phosphate and 0.1 parts of diethyl maleate weredissolved in 10 parts of ethyl acetate. This solution was introducedinto a solution in which 20 parts of a 6% aqueous solution of gelatinand 2 parts of a 2% aqueous solution of sodium dodecylsulfonate had beenmixed. This was emulsified for 10 minutes with a homogenizer. Thus, theemulsion dispersion of the developer was obtained.

[0304] Preparation of the Coating Liquid

[0305] To the electron-donating dye precursor-encasing microcapsulesolution prepared earlier was added an SBR latex (SN-307, produced bySumitomo Naugatuck Co. Ltd.) in an amount of 40% relative to capsulesolids. To this solution was added the emulsion dispersion of thedeveloper in a weight ratio (the emulsion dispersion: theelectron-donating dye precursor-encasing microcapsule solution) of 1:4.Thus, the coating liquid for the cyan heat-sensitive recording layer wasobtained.

[0306] 4) Preparation of a Coating Liquid for a Magenta Heat-SensitiveRecording Layer

[0307] Preparation of Diazo Compound-Encasing Microcapsule Liquid (i)

[0308] 2.0 parts of diazo compound (1) (decomposable by light with awavelength of 365 nm), shown below, was dissolved in 20 parts of ethylacetate. Then, 20 parts of alkylnaphthalene was added, and this mixturewas heated and mixed homogeneously. To the resulting solution was added15 parts of a 1:3-weighted adduct of xylylene diisocyanate andtrimethylol propane (a capsule wall agent). The solution washomogeneously stirred and a diazo compound solution was obtained.

[0309] The diazo compound solution was added to a solution in which 54parts of a 6% aqueous solution of phthalated gelatin and 2 parts of a 2%aqueous solution of sodium dodecylsulfonate had been mixed. This wasemulsion-dispersed using a homogenizer. Next, 68 parts of water wasadded to the resulting emulsion dispersion and homogeneously mixed. Thenthis mixture was heated to 40 ° C. while being stirred. An encapsulationreaction was carried out for 3 hours so as to produce microcapsuleshaving a mean particle size of 1.2 μm. Thus, diazo compound-encasingmicrocapsule liquid (i) was obtained.

[0310] Preparation of Coupler Emulsion Dispersion (i)

[0311] 2 parts of coupler (1), shown below, 2 parts of 1,2,3-triphenylguanidine, 0.3 parts of tricresyl phosphate and 0.1 parts of diethylmaleate were dissolved in 10 parts of ethyl acetate. This solution wasintroduced into a solution in which 20 parts of a 6% aqueous solution ofgelatin and 2 parts of a 2% aqueous solution of sodium dodecylsulfonatehad been mixed. This was emulsified for 10 minutes with a homogenizer.Thus, coupler emulsion dispersion (i) was obtained.

[0312] Preparation of the Coating Liquid

[0313] To diazo compound-encasing microcapsule liquid (i) preparedearlier was added an SBR latex (SN-307, produced by Sumitomo NaugatuckCo. Ltd.) in an amount of 40% relative to capsule solids. Then, thecoupler emulsion dispersion (i) was mixed with the diazocompound-encasing microcapsule liquid (i) in a weight ratio of 3:2.Thus, the coating liquid for the magenta heat-sensitive recording layerwas obtained.

[0314] 5) Preparation of a Coating Liquid for a Yellow Heat-SensitiveRecording Layer

[0315] Preparation of Diazo Compound-Encasing Microcapsule Liquid (ii)

[0316] 3.0 parts of 2,5-dibutoxy-4-tolylthiobenzenediazoniumhexafluorophosphate (a diazo compound: decomposable by light with awavelength of 420 nm) was dissolved in 20 parts of ethyl acetate. Then20 parts of alkylnaphthalene, a high-boiling-point solvent, was addedthereto, and this mixture was heated and mixed homogeneously.

[0317] To the resulting solution was added 15 parts of a 1:3 weightedadduct of xylylene diisocyanate and trimethylol. The solution washomogeneously stirred and a diazo compound solution was obtained.

[0318] The diazo compound solution was added to a solution in which 54parts of a 6% aqueous solution of phthalated gelatin and 2 parts of a 2%aqueous solution of sodium dodecylsulfonate had been mixed. This wasemulsion-dispersed using a homogenizer. Next, 68 parts of water wasadded to the resulting emulsion dispersion and homogeneously mixed. Thenthis mixture was heated to 40 ° C. while being stirred. An encapsulationreaction was carried out for 3 hours so as to produce microcapsuleshaving a mean particle size of 1.3 μm. Thus, diazo compound-encasingmicrocapsule liquid (ii) was obtained.

[0319] Preparation of Coupler Emulsion Dispersion (ii)

[0320] 2 parts of2-chlor/-5-(3-(2,4-di-tert-pentyl)phenoxypropylamino)acetoacetanilide, 1part of 1,2,3-triphenyl guanidine, 0.3 parts of tricresyl phosphate and0.1 parts of diethyl maleate were dissolved in 10 parts of ethylacetate. This solution was introduced into a solution in which 20 partsof a 6% aqueous solution of gelatin and 2 parts of a 2% aqueous solutionof sodium dodecylsulfonate had been mixed. This was emulsified for 10minutes with a homogenizer. Thus, coupler emulsion dispersion (ii) wasobtained.

[0321] Preparation of the Coating Liquid

[0322] The coupler emulsion dispersion (ii) was mixed with the diazocompound-encasing microcapsule liquid (ii) in a weight ratio of 3:2.Thus, the coating liquid for the yellow heat-sensitive recording layerwas obtained.

[0323] 6) Preparation of an Intermediate Layer Coating Liquid

[0324] 10 parts of a 15% aqueous solution of gelatin (#750, produced byNitta Gelatin Inc.) and 3 parts of a 15% aqueous solution of polyacrylicacid (JULIMER AC-10L, produced by Nippon Junyaku Co., Ltd.) werehomogeneously mixed together, and the intermediate layer coating liquidwas obtained.

[0325] 7) Preparation of a Transmittance-Regulating Layer Coating Liquid

[0326] 1.5 parts of the compound shown below, 0.5 parts of followingcompound R-6 as a reducing agent and 0.8 parts of tricresyl phosphatewere thoroughly mixed and dissolved in 6.0 parts of ethyl acetate. Tothe resulting solution was added 3.0 parts of an adduct of xylylenediisocyanate and trimethylol propane (75% ethyl acetate solution,tradename: TAKENATE D110ON, produced by Takeda Chemical Industries,Ltd.) as a capsule wall-forming agent. The solution was homogeneouslystirred, 29.7 parts of an 8% aqueous solution of carboxy-denaturedpolyvinyl alcohol (KL-318, produced by Kuraray Co., Ltd.) was addedthereto, and emulsion-dispersion was performed with a homogenizer.

[0327] The resulting emulsion was added to 40 parts of ion-exchangewater, and stirred for 3 hours at 40 ° C. to carry out an encapsulationreaction. 7.0 parts of ion-exchange resin was added, and the stirringwas continued for a further 1 hour. Thus, the transmittance-regulatinglayer coating liquid was obtained. The mean particle size of thecapsules was 0.35 μm.

[0328] 8) Preparation of Protective Layer Coating Liquid (1)

[0329] The compounds of the following composition were mixed, andprotective layer coating liquid (1) was obtained. Composition EP130 (7%)100 g (dodecyl-denatured polyvinyl alcohol, produced by Denki KagakuKogyo, K.K.) Water 50 g SILICA MICROBEAD P500 dispersion (20%) 10 g(microparticle-aggregation particles, produced by Catalyst & ChemicalsInd. Co., Ltd. mean particle size of the microparticle aggregationparticles: 1.8 μm, Mohs′ hardness: 7) Aforementioned surfactant-1 (2%) 5ml Following surfactant-2 (5%) 5 ml Zinc stearate dispersion (20%) 3 gSurfactant-2

[0330] 9) Fabrication of a Heat-Sensitive Recording Material

[0331] A plurality of layers was coated onto the front face of thepolyethylene-laminated paper substrate in the following order (from thesubstrate side): the undercoat layer coating liquid, the cyanheat-sensitive recording layer coating liquid, the intermediate layercoating liquid, the magenta heat-sensitive recording layer coatingliquid, the intermediate layer coating liquid, the yellow heat-sensitiverecording layer coating liquid, the transmittance-regulating layercoating liquid, and the protective layer coating liquid. The layers weredried, and a multi-color heat-sensitive recording material (1) of thepresent invention was obtained.

[0332] A coating amount of each layer was calculated for solids afterdrying: 1.0 g/m² for the undercoat layer, 6.1 g/m² for the cyanheat-sensitive recording layer, 1.0 g/m² for one of the intermediatelayers, 7.8 g/m² for the magenta heat-sensitive recording layer, 1.0g/m² for another of the intermediate layers, 7.2 g/m² for the yellowheat-sensitive recording layer, 1.5 g/m² for thetransmittance-regulating layer, and 1.2 g/m² for the protective layer.

Example 2

[0333]8′) Preparation of Protective Layer Coating Liquid (2)

[0334] The compounds of the following composition were mixed, andprotective layer coating liquid (2) was prepared. Then, a multi-colorheat-sensitive recording material (2) of the present invention wasprepared in the same way as for Example 1, except that protective layercoating liquid (2) was used in place of the protective layer coatingliquid (1) that was used in Example 1. Composition EP130 (7%) 100 g(dodecyl-denatured polyvinyl alcohol, produced by Denki Kagaku Kogyo,K.K.) Water 52 g BARIFINE BF 21 dispersion (20%) 5 g (barium sulfatemicroparticles, produced by Sakai Chemical Industry Co., Ltd.) SILICAMICROBEAD P500 dispersion (20%) 5 g (microparticle-aggregationparticles, produced by Catalyst & Chemicals Ind. Co., Ltd.)Aforementioned surfactant-1 (2%) 10 ml Aforementioned surfactant-2 (5%)10 ml Zinc stearate dispersion (20%) 3 g

Comparative Example 1

[0335] A protective layer coating liquid (3) was prepared in the sameway as protective layer coating liquid (1), except that a BARIFINE BF21(20%) dispersion (barium sulfate microparticles, produced by SakaiChemical Industry Co., Ltd.) was used in place of the SILICA MICROBEADP500 (20%) dispersion (microparticle-aggregation particles) that wasused in preparing protective layer coating liquid (1) in Example 1.

[0336] A Comparative Example multi-color heat-sensitive recordingmaterial (3) was prepared in the same way as for Example 1, except thatprotective layer coating liquid (3) was used in place of the protectivelayer coating liquid (1) that was used in Example 1.

Comparative Example 2

[0337] A protective layer coating liquid (4) was prepared in the sameway as protective layer coating liquid (1), except that SNOWTEX C (20%)(colloidal silica dispersion, produced by Nissan Chemical Industries,Ltd.) was used in place of the SILICA MICROBEAD P500 (20%) dispersion(microparticle-aggregation particles) that was used in preparingprotective layer coating liquid (1) in Example 1.

[0338] A Comparative Example multi-color heat-sensitive recordingmaterial (4) was prepared in the same way as for Example 1, except thatprotective layer coating liquid (4) was used in place of the protectivelayer coating liquid (1) that was used in Example 1.

Comparative Example 3

[0339]8″) Preparation of a Protective Layer Coating liquid

[0340] The compounds of the following composition were mixed, andprotective layer coating liquid (5) was prepared. Then, a ComparativeExample multi-color heat-sensitive recording material (5) was preparedin the same way as for Example 1, except that protective layer coatingliquid (5) was used in place of the protective layer coating liquid (1)that was used in Example 1. Composition EP130 (7%) 100 g(dodecyl-denatured polyvinyl alcohol, produced by Denki Kagaku Kogyo,K.K.) Water 50 g SILTON AMT-25 dispersion (20%) 10 g (aluminosilicate,mean particle size 2 μm, produced by Mizusawa Chemical Co., Ltd.)Aforementioned surfactant-1 (2%) 10 ml Aforementioned surfactant-2 (5%)10 ml Dialdehyde starch (5%) 14 g p-toluene sulfonic acid (10%) 0.7 gZinc stearate dispersion (20%) 3 g

Comparative Example 4

[0341] A protective layer coating liquid (6) was prepared in the sameway as protective layer coating liquid (5), except that SILTONAMT-SILICA #300 (20%) (mean particle size 3 μm, produced by MizusawaChemical Co., Ltd.) was used in place of the SILTON AMT-25 (20%)dispersion that was used in preparing the protective layer coatingliquid (5) used in Comparative Example 3.

[0342] A Comparative Example multi-color heat-sensitive recordingmaterial (6) was prepared in the same way as for Example 1, except thatprotective layer coating liquid (6) was used in place of the protectivelayer coating liquid (1) that was used in Example 1.

[0343] Head-Soiling Evaluation

[0344] Using an NC370D digital printer, manufactured by Fuji Photo FilmCo., Ltd., an image was continuously printed on 500 sheets with printingtemperatures in each of a low temperature range, a medium temperaturerange and a high temperature range. Then the thermal head of the printerwas examined with an optical microscope. Soiling condition was evaluatedin accordance with three levels, from A (good) to C (bad). Evaluationresults are shown in table 1 below.

[0345] Head-Wearing Evaluation

[0346] Using an NC370D digital printer manufactured by Fuji Photo FilmCo., Ltd., an image was continuously printed on 10,000 sheets withprinting temperatures in each of a low temperature range, a mediumtemperature range and a high temperature range. Then a printing portionof the thermal head of the printer was measured with a laser-typesurface contour measuring device. A degree of wearing was evaluated inaccordance with three levels, from A (slight) to C (severe). Evaluationresults are shown in table 1 below.

[0347] Homogeneity of Image Density

[0348] A large number of sheets were continuously printed. At1,000-sheet intervals, a solid gray image was printed. A degree ofprinted image density unevenness, caused by head-soiling andhead-wearing of the thermal head and the like, was evaluated therefromin accordance with three levels, from A (slight) to C (severe).Evaluation results are shown in table 1 below. TABLE 1 Heat-sensitiveHead- Head- Image recording material soiling wearing homogeneity Example1 (1) A A A Example 2 (2) A A A Comparative (3) B A A/B Example 1Comparative (4) A C A/B Example 2 Comparative (5) A C A/B Example 3Comparative (6) A C A/B Example 4

[0349] From the results of table 1 it can be seen that heat-sensitiverecording materials 1 and 2, which contained microparticle-aggregationparticles in the outermost layer, namely, the protective layer, wereexcellent in both head-soiling and head-wearing, and could stably printuniform images with no unevenness of density. In contrast,heat-sensitive recording materials 3 to 6, which did not containmicroparticle-aggregation particles in the outermost layer, could notavoid head-soiling and avoid head-wearing, and unevenness of density wasdiscernible.

What is claimed is:
 1. A heat-sensitive recording material having aheat-sensitive recording layer on a substrate, wherein an outermostlayer on the substrate contains microparticle-aggregation particles. 2.The heat-sensitive recording material of claim 1, wherein themicroparticle-aggregation particles are composed of inorganicmicroparticles.
 3. The heat-sensitive recording material of claim 2,wherein the inorganic microparticles are silica microparticles.
 4. Theheat-sensitive recording material of claim 1, wherein the outermostlayer is a protective layer.
 5. The heat-sensitive recording material ofclaim 2, wherein the outermost layer is a protective layer.
 6. Theheat-sensitive recording material of claim 3, wherein the outermostlayer is a protective layer.
 7. The heat-sensitive recording material ofclaim 1, wherein the microparticle-aggregation particles have a Mohs'hardness of from 2 to
 8. 8. The heat-sensitive recording material ofclaim 2, wherein the microparticle-aggregation particles have a Mohs'hardness of from 2 to
 8. 9. The heat-sensitive recording material ofclaim 3, wherein the microparticle-aggregation particles have a Mohs'hardness of from 2 to
 8. 10. The heat-sensitive recording material ofclaim 1, wherein mean particle size of the microparticle-aggregationparticles is from 0.5 to 10 μm.
 11. The heat-sensitive recordingmaterial of claim 2, wherein mean particle size of themicroparticle-aggregation particles is from 0.5 to 10 μm.
 12. Theheat-sensitive recording material of claim 3, wherein mean particle sizeof the microparticle-aggregation particles is from 0.5 to 10 μm.
 13. Theheat-sensitive recording material of claim 1, wherein an amount of themicroparticle-aggregation particles in the outermost layer is from 0.01to 1.0 g/m².
 14. The heat-sensitive recording material of claim 2,wherein an amount of the microparticle-aggregation particles in theoutermost layer is from 0.01 to 1.0 g/m².
 15. The heat-sensitiverecording material of claim 3, wherein an amount of themicroparticle-aggregation particles in the outermost layer is from 0.01to 1.0 g/m².
 16. The heat-sensitive recording material of claim 4,wherein an amount of the microparticle-aggregation particles in theoutermost layer is from 0.01 to 1.0 g/m².